NMR logging apparatus

ABSTRACT

Technologies including NMR logging apparatus and methods are disclosed. Example NMR logging apparatus may include surface instrumentation and one or more downhole probes configured to fit within an earth borehole. The surface instrumentation may comprise a power amplifier, which may be coupled to the downhole probes via one or more transmission lines, and a controller configured to cause the power amplifier to generate a NMR activating pulse or sequence of pulses. Impedance matching means may be configured to match an output impedance of the power amplifier through a transmission line to a load impedance of a downhole probe. Methods may include deploying the various elements of disclosed NMR logging apparatus and using the apparatus to perform NMR measurements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is divisional of U.S. patent application Ser. No.13/356,381, entitled “NMR LOGGING APPARATUS”, filed on Jan. 23, 2012,issued as U.S. Pat. No. 8,736,264.

STATEMENT OF GOVERNMENT SUPPORT

This invention was made in part with Government support under AgreementDE-FG02-07ER84931 awarded by the US Department of Energy. The Governmenthas certain rights in this invention.

BACKGROUND

Nuclear Magnetic Resonance (NMR) systems have been in use for many yearsand can be used to provide imaging and/or analysis of a sample beingtested. For example, U.S. Pat. No. 6,160,398, U.S. Pat. No. 7,466,128,U.S. Pat. No. 7,986,143, U.S. patent application Ser. No. 12/914,138,and U.S. patent application Ser. No. 13/104,721 describe a variety ofNMR technologies, and are incorporated herein by reference. Variousdifferent types of NMR include medical NMR, often referred to asMagnetic Resonance Imaging (MRI), and NMR for measuring properties ofearth formations, which provides, for example, geophysical techniquesfor detecting properties of the earth's crust. This disclosure relatesto the latter type of NMR, and so the term “NMR” as used herein refersto NMR in the geophysical context. While there is some overlap in thetechnologies that may be applied in MRI and NMR, the samples beingmeasured and the environments in which measurements are performed aredifferent, leading to many differences in the technologies applied.

In general, NMR measurement involves generating a static magnetic fieldwithin a sample volume, emitting Radio-Frequency (RF) electromagneticpulses into the sample volume, and detecting RF NMR responses from thesample volume. Most commonly, NMR measurement involves emitting multipleRF pulses in rapid succession and measuring the RF NMR responses betweenthe RF pulses. The measured RF NMR responses provide useful informationabout the sample volume.

NMR measurements may be used to detect properties including, forexample, the abundance of hydrogen contained within a sample volume aswell as fluid composition, porosity, and permeability of the samplevolume. NMR measurements may also be used to detect certain other atomicspecies, including carbon and potassium.

The term NMR as used herein includes Nuclear Quadrupole Resonance (NQR),unless stated otherwise. NQR is often useful for detecting nitrogen,chlorine and other compounds. NQR measurement techniques are similar tothose used for NMR in general. While NMR measurements generally includegenerating a static magnetic field, a static magnetic field is notalways required or used for NQR measurements.

NMR logging is an established type of surface NMR measurement wherein anNMR measurement apparatus is lowered into a borehole in the earth, andNMR measurements are performed to determine properties within and/orsurrounding the borehole. However, existing NMR logging apparatus have anumber of drawbacks, including high expense and difficulty of operation.

For example, some previous NMR logging apparatus may include most or allapparatus components, including for example a controller, a powersupply, a power amplifier, transmit and receive antennae, and Analog toDigital (A/D) converter(s), within a downhole sensor package designed tofit within a borehole. Such a downhole sensor package may be 5 inches orlarger in diameter and may weigh from several hundred pounds to over onethousand pounds.

In addition to size and weight limitations, previous NMR loggingapparatus do not enable economical long-term or wide area in-situmonitoring of subsurface properties. Long-term or wide area in-situmonitoring is uneconomical when many expensive components are includedwithin a downhole sensor package, because either many expensive NMRlogging apparatus must be purchased, or expensive components must beeither left in place long-term, and therefore unavailable for otheruses, or NMR logging apparatus must be repeatedly mobilized whichinvolves mobilization and human labor costs.

SUMMARY

Technologies applicable to NMR logging are disclosed. Some example NMRlogging apparatus may comprise surface instrumentation coupled to adownhole probe via a transmission line. The surface instrumentation maycomprise a controller, a signal generator, a power supply, a poweramplifier configured to generate one or more current and/or voltagewaveforms, and receive electronics such as A/D converter(s) and memoryfor storing digitized NMR response data. The transmission line may becoupled with the power amplifier and may have a length at least onetenth of one wavelength of a current and/or voltage waveform generatedby the power amplifier. The downhole probe may be configured to fitwithin an earth borehole, and may comprise one or more static magneticfield generation devices, such as one or more magnets, and one or moreantennae coupled with the transmission line.

Example NMR logging apparatus may also include an impedance matchingmeans configured to match an output impedance of the power amplifierthrough the transmission line to a load impedance of one or more of theantennae in the downhole probe. Impedance matching means may comprise afirst matching means configured to match the output impedance of thepower amplifier to a characteristic impedance of the transmission line,and/or a second matching means configured to match load impedance of oneor more antennae in the downhole probe to the characteristic impedanceof the transmission line. The first and/or second matching means maycomprise an impedance matching circuit comprising transformers,combinations of inductors and capacitors, or combinations oftransformers, inductors and capacitors. Impedance matching means maycomprise a transmission line length that is approximately a positiveinteger number of quarter wavelengths of a current and/or voltagewaveform generated by the power amplifier. Impedance matching means maycomprise one or more antennae in the downhole probe that are configuredto present a load impedance approximately equal to a characteristicimpedance of the transmission line during a transmit mode.

An example downhole probe may comprise means for detecting NMR signalsinduced in the antennae. A preamplifier may be configured to amplifydetected NMR signals. In some embodiments, an output impedance of thepreamplifier may be matched to a characteristic impedance of a secondtransmission line configured to transmit detected NMR signals from thedownhole probe to the surface instrumentation. A downhole probe may alsocomprise one or more Analog to Digital (A/D) converter(s). Electronicswithin a downhole probe may be coupled with a power supply on thesurface, or may comprise a local power supply such as one or morebatteries.

In some embodiments, a plurality of downhole probes may be coupled withthe power amplifier via a plurality of transmission lines, and thesurface instrumentation may be configured to perform NMR measurementswith the plurality of downhole probes. A switching device may be coupledbetween the plurality of transmission lines and the power amplifier, andthe switching device may be configured to selectively connect the poweramplifier to one or more of the transmission lines.

Some example NMR measurement methods may include deploying surfaceinstrumentation on or above the surface of the earth, the surfaceinstrumentation comprising a controller and power amplifier configuredto generate one or more NMR-activating current and/or voltage waveforms;deploying a downhole probe inside an earth borehole, the downhole probecomprising one or more antennae, and detection means configured todetect NMR signals induced on the antennae; deploying a transmissionline configured to transfer a current and/or voltage waveform betweenthe power amplifier and the downhole probe, the transmission line havinga physical length equal to or greater than one tenth of the wavelengthof the transferred current and/or voltage waveform within thetransmission line; deploying an impedance matching means at one or bothends of the transmission line, the impedance matching means configuredto match an output impedance of the power amplifier through thetransmission line to a load impedance of one or more of the antennae inthe downhole probe during a transmit mode; and using the surfaceinstrumentation and downhole probe coupled via the transmission line andimpedance matching means to perform NMR measurements of one or moreproperties within and/or surrounding the earth borehole. The one or moreproperties may include NQR properties, which are one type of NMRproperty as described herein.

Some example NMR measurement methods may include deploying surfaceinstrumentation on or above the surface of the earth, the surfaceinstrumentation comprising a controller and power amplifier configuredto generate one or more NMR activating current and/or voltage waveforms;deploying a plurality of downhole probes inside one or more earthboreholes, each of the downhole probes comprising one or more antennae,and detection means configured to detect NMR signals; deploying aplurality of transmission lines configured to transfer current and/orvoltage waveforms between the power amplifier and the downhole probes;and using the surface instrumentation and downhole probes coupled viathe transmission lines to perform NMR measurements of one or moreproperties within and/or surrounding the earth borehole(s). In someembodiments, at least one of the transmission lines may have a physicallength equal to or greater than one tenth of the wavelength of a currentand/or voltage waveform, and an impedance matching means may be deployedto match an output impedance of the power amplifier through the at leastone transmission line to a load impedance of one or more of the antennaein a downhole probe during a transmit mode of the surfaceinstrumentation.

Some example NMR measurement methods may include using at least one ofthe downhole probes to perform a plurality of NMR measurements at a samelocation in an earth borehole, wherein the measurements are separated intime. The plurality of NMR measurements may be used to detect a changeover time of measured properties. Measured properties may include, e.g.,NMR properties, NQR properties, physical properties, hydraulicproperties, or chemical properties.

Further aspects and variations are discussed in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features and attendant advantages of the disclosed technologieswill become fully appreciated when considered in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the several views, and wherein:

FIG. 1 illustrates an example NMR logging apparatus and locations ofcomponents thereof relative to the surface of the earth;

FIG. 2 illustrates an example downhole probe including separatetransmitting and receiving antennae;

FIG. 3 illustrates an example downhole probe including a combinationtransmitting/receiving antenna;

FIG. 4 illustrates an example downhole probe including a receive circuitmatching means configured to match load impedance of one or moreantennae in a downhole probe to a characteristic impedance of atransmission line;

FIG. 5 illustrates an example impedance matching means comprising one ormore impedance matching circuits;

FIG. 6 illustrates an example impedance matching means comprising one ormore impedance matching circuits;

FIG. 7 illustrates an example impedance matching means comprising one ormore impedance matching circuits;

FIG. 8 illustrates an example impedance matching means comprising one ormore impedance matching circuits;

FIG. 9 illustrates an example NMR logging apparatus comprising surfaceinstrumentation, a plurality of transmission lines, and a plurality ofdownhole probes; and

FIG. 10 illustrates an example NMR logging apparatus comprising surfaceinstrumentation, a plurality of transmission lines, a plurality ofdownhole probes, and a switching device coupled between the transmissionlines and the power amplifier to selectively connect the power amplifierto one or more of the transmission lines.

DETAILED DESCRIPTION

Prior to explaining embodiments of the invention in detail, it is to beunderstood that the invention is not limited to the details ofconstruction or arrangements of the components and method steps setforth in the following description or illustrated in the drawings. Theinvention is capable of other embodiments and of being practiced andcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein are for the purpose of thedescription and should not be regarded as limiting.

Technologies including NMR logging apparatus and methods are disclosed.Example NMR logging apparatus may include surface instrumentation andone or more downhole probes configured to fit within an earth borehole.The surface instrumentation may comprise a power amplifier, which may becoupled to the downhole probes via one or more transmission lines, and acontroller configured to cause the power amplifier to generate a NMRactivating pulse or sequence of pulses. Impedance matching means may beconfigured to match an output impedance of the power amplifier through atransmission line to a load impedance of a downhole probe. Methods mayinclude deploying the various elements of disclosed NMR loggingapparatus and using deployed NMR logging apparatus to perform NMRmeasurements.

FIG. 1 illustrates an example NMR logging apparatus and locations ofcomponents thereof relative to the surface of the earth, in accordancewith various embodiments of this disclosure. The NMR logging apparatusin FIG. 1 includes: surface instrumentation (1), located near thesurface of the earth; a downhole probe (2) which is lowered into anearth borehole (3) to measure properties of within and/or surroundingthe borehole, e.g., properties of earth formation (4), and anelectrically long transmission line (5) with impedance matching means (6a, 6 b) at one or both ends of the transmission line (5). An optionaldraw works (7) may be employed to deploy and retrieve the transmissionline (5) and downhole probe (2). In some embodiments, the illustratedNMR logging apparatus may be configured to perform NMR measurements, forexample to characterize subsurface fluids and geologic formations.

The surface instrumentation (1) includes a controller (10) such as acomputer or digital processor which is programmed to produce NMR pulsesequences appropriate and useful for performing NMR measurements inearth formations. The controller may also control other aspects of NMRmeasurement, such as by controlling switches such as the switch (22)illustrated in FIG. 2 and the switching device (7) illustrated in FIG.10.

In some embodiments, NMR pulse sequences may comprise a CPMG sequence inwhich a series of pulses are generated, separated by a duration(“echo-time”) that may be on the order of a two milliseconds or shorter.The echo-time spacing may be short to optimize the signal to noise ratioand to reduce artifacts associated with molecular diffusion in fluids.Using a short-echo time, however, increases the effective duty cycleplaced on the power generation components (11, 13) and so the powergeneration components (11, 13) may be configured to support short-echotimes in some embodiments. For example, long term power capacity of anNMR logging apparatus may be increased by adding energy storagecapacitors to the surface instrumentation (1).

The surface instrumentation (1) may include an appropriate power supply(11) to power the various components of the surface instrumentation (1),and optionally also the downhole probe (2).

The surface instrumentation (1) also includes digital and/or analogoutput signal generator (12), which may be controlled by the controller(10), and which may produce low voltage NMR pulse sequence activatingsignals as input to the power amplifier (13). In some embodiments, asignal generator (12) may be implemented by the controller (10) or aseparate signal generator device.

The surface instrumentation (1) may also include a power amplifier (13)configured to produce amplified NMR excitation waveforms as currentand/or voltage waveforms. The power amplifier (13) may be configured touse signals produced by signal generator (12) and power from the powersupply (11) to produce amplified signals. Areas directly surrounding adownhole probe (2) may contain fluids in the borehole annulus (3) orregions of the earth formation (4) surrounding the borehole (3) thatwere disturbed during drilling. Therefore it may be preferable in somecircumstances to investigate a zone several inches or more away from thecenter of the downhole probe (2). RF fields generated by passingamplified RF current through downhole probe antennae decrease inamplitude further from the downhole probe (2) due to geometricattenuation. Therefore power supplies for a downhole probe (2) may, insome circumstances, be capable of generating sufficiently high currentpulses for the RF fields to penetrate the earth formation (4). Hence, itis preferable in some NMR logging apparatus to employ a power amplifier(13) capable of producing peak power of 2 kW or higher.

The surface instrumentation (1) may include receive electronics such asA/D converter (14) configured to convert NMR response signals receivedfrom the downhole probe (2) from analog to digital form, and a memory 15configured to store digitized NMR response data. Digitized NMR responsedata may be stored in a memory (15), such as a memory in a computer, andmay be processed and analyzed in a variety of useful ways. The memory(15) may in some embodiments be included in a computer along withcontroller (10), and such a computer may also comprise software foranalysis of received NMR response data.

Depending on the specific embodiment, A/D converters (14) may be locatedat the surface or with downhole probe electronics. In embodiment whereinA/D converters (14) are located at the surface, a second electricallylong transmission line (such as 5 b in FIG. 2) may be used to transmitan analog receive signal from the downhole probe to the surface, andimpedance matching means may be used to maximize the efficiency oftransmission of the receive signal from the downhole probe (2) to thesurface. In embodiments wherein the A/D converters (14) are locatedwithin the downhole probe (2), the A/D converters (14) may be configuredto operate automatically, or the surface instrumentation (1) maycomprise a controller (such as controller (10) or a separate controller)configured to remotely control the one or more A/D converters (14) inthe downhole probe (2). A controller may be configured to synchronizeoperation of A/D converters (14) with a transmit cycle though anauxiliary clock line extending to downhole probe (2), or thoughbootstrap clock signals and/or triggers combined with a transmitted NMRpulse sequence.

The transmission line (5) may be an electrical transmission line withcharacteristic impedance Zo. The term “electrically long” as used hereinrefers to a physical length greater than one tenth of a wavelength of acurrent and/or voltage waveform produced by the power amplifier (13) ata transmitting operating frequency. This is the approximate the lengthat which wave reflections and phase delays become significant.

The impedance matching means (6 a, 6 b) employed at one or both ends ofthe transmission line (5) may be configured to approximately match theload impedance Zl of transmitting antennae in the downhole probe (2), asseen through the transmission line (5), to the output impedance Zs ofthe surface-based power amplifier (13).

The downhole probe (2) may be designed to fit in a cased or uncasedearth borehole, and may contain a magnet assembly configured to generatean elevated static background magnetic field in a sample volume withinearth formation (4), one or more antennae configured to use theamplified excitation waveforms to emit RF signals into the sample volumewithin earth formation (4), and one or more antennae configured todetect an NMR response from the sample volume within earth formation(4).

In some embodiments, tuning capacitors may be included at the surfaceand/or within the downhole probe (2) to maximize power transfer betweenthe surface based power amplifier (13) and the downhole probe antennae.

In some embodiments, NMR logging apparatus according to this disclosuremay be configured for use with small and very small diameter boreholes.A small diameter borehole is defined herein as less than 5 inches indiameter, and a very small diameter borehole is defined herein as 2inches or less in diameter. Therefore some downhole probes according tothis disclosure may be either less than 5 inches in diameter or 2 inchesor less in diameter, depending on the specific embodiment. Additionally,downhole probes according to this disclosure may be configured with lowweight, e.g., less than 100 pounds, and relatively low production cost.

FIG. 2 illustrates an example downhole probe (2) including separatetransmitting and receiving antennae, in accordance with variousembodiments of this disclosure. FIG. 2 includes a downhole probe (2)comprising a matching means (6 b), a transmitting antenna (21 a), anarray of one or more static magnetic field generating devices (20), areceiving antenna (21 b) including tuning capacitors (27), atransmit/receive switch (22), and a preamplifier (23). A transmissionline (5 a) is coupled with transmitting antenna (21 a) via matchingmeans (6 b). A second transmission line (5 b) is coupled with receivingantenna (21 b) via transmit/receive switch (22) and preamplifier (23).

In some embodiments, multiple transmission lines (5 a, 5 b) may be used.A first transmission line (5 a) may couple a transmitting antenna (21 a)in the downhole probe (2) with a surface based power amplifier (13). Asecond transmission line (5 b) may couple a receiving antenna (21 b) inthe downhole probe (2) with surface based receive electronics, such as asurface based A/D converter (14). Either or both of the transmissionlines (5 a, 5 b) may be electrically long transmission lines, and eitheror both of the transmission lines (5 a, 5 b) may be coupled withimpedance matching means, as described herein. In some embodiments,differently configured impedance matching means may be employed fordifferent transmission lines (5 a, 5 b). Either or both of thetransmission lines (5 a, 5 b) may comprise a cable in some embodiments.

Depending upon the impedance matching means selected for a particularembodiment of the invention, matching means (6 b) may be incorporatedwithin the downhole probe (2) to perform some or all of the impedancematching between the transmission line (5 a), the transmitting antenna(21 a), and the surface based power amplifier (13).

The downhole probe (2) may include an array of one or more staticmagnetic field generating devices (20). Magnetic field generatingdevices (20) may include permanent magnets and/or electromagnets.

The downhole probe (2) may include a transmitting antenna (21 a) whichis configured to generate RF magnetic fields during a transmit mode tocause precession of NMR active nuclei, and a receiving antenna (21 b)which is configured to detect the resulting magnetic fields generated bythe NMR processes during a receive mode. Transmitting and receivingfunctions may be accomplished by a same antenna, or by separatetransmitting and receiving antennae as shown in FIG. 2.

The antennae (21 a) and (21 b) may be single turn, or multiple turninduction loops, also referred to herein as current loops and/or coils,and may also be partial coaxial type antennae, or any other type ofantenna or induction coil suitable for generating RF magnetic fields inan earth formation and for detecting NMR responses from an earthformation. The antennae (21 a) and (21 b) may optionally include tuningcapacitors (27) or other appropriate tuning mechanisms. In someembodiments, the transmitting antenna (21 a) and receiving antenna (21b) may be inductively coupled with a non-zero mutual inductance during atransmit mode, as described further herein.

The downhole probe (2) may include a transmit/receive switch (22) toisolate receive electronics such as the preamplifier (23) and otherreceive electronics that may be coupled therewith, from high voltage onthe receiving antenna (21 b) during transmit mode, and to couple thereceiving antenna (21 b) to the receive electronics during receive mode.

The downhole probe (2) may include a preamplifier (23) to amplify todetected NMR signals to suitable levels for digitization and/or foranalog transmission to surface instrumentation (1). The transmit/receiveswitch (22) and preamplifier (23) are example means for detecting NMRsignals induced in at least one of the antennae in the downhole probe(2). In some embodiments, an output impedance of the preamplifier (23)may be matched to a characteristic impedance of the second transmissionline (5 b).

The downhole probe (2) may comprise means for coupling energy from thetransmission lines (5 a, 5 b) into at least one of the antennae (21 a,21 b). For example, an electrical interface (not shown) may beconfigured to connect and disconnect the transmission lines (5 a, 5 b)from the downhole probe (2), so the components can be separated fortransport and storage.

In some embodiments, the downhole probe (2) may include a means (notshown) for reducing the Q-factor of the transmitting and/or receivingantennae (21 a, 21 b). This Q-damping means may comprise passiveelectronics and/or actively controlled electronics circuits. TheQ-damping electronics circuits may be electrically connected to one ormore of the receiving antenna, for example as described in U.S. Pat. No.5,055,788, or inductively coupled to one or more of the transmittingand/or receiving antennae as described in U.S. Pat. No. 6,291,994. TheQ-damping means may be active during either all or part of the transmitmode, during all or part of the receive mode, or during part or all ofboth modes. Passive Q-damping circuits may include diode-based circuitsthat increase effective circuit resistance when a transmitting voltageexceeds a diode turn-on voltage. Actively controlled Q-damping circuitsmay be controlled via external timing from a surface-based controller,such as controller (10), or automatically triggered from the timing of atransmitted pulse sequence.

FIG. 3 illustrates an example downhole probe including a combinationtransmitting/receiving antenna, in accordance with various embodimentsof this disclosure. FIG. 3 includes a downhole probe (2) comprising amatching means (6 b), transmitting/receiving antenna (21) configured toperform both transmitting and receiving functions and including tuningcapacitors (27), an array of one or more static magnetic fieldgenerating devices (20), a transmit/receive switch (22), and apreamplifier (23). A transmission line (5 a) is coupled withtransmitting/receiving antenna (21) via matching means (6 b). A secondtransmission line (5 b) is coupled with transmitting/receiving antenna(21) via transmit/receive switch (22) and preamplifier (23).

In FIG. 3, matching means (6 b) may be configured to perform some or allof the impedance matching between the transmitting/receiving antenna(21), the transmission line (5 a), and the surface based power amplifier(13). In FIG. 2 and FIG. 3, the static magnetic field generating devices(20) and the transmitting and receiving antennae (21, 21 a, 21 b) may bearranged and designed in any form that is useful and convenient formeasuring NMR properties of an earth formation. This disclosure is notdependent on any specific arrangement of magnets and antennae.Embodiments may utilize any magnet and antenna designs known in the artor as may be developed in the future. For example, designs disclosed inU.S. Pat. No. 4,710,713 and U.S. Pat. No. 5,055,788, may be applied inthe context of some embodiments of the present disclosure,

FIG. 4 illustrates an example downhole probe including a receive circuitmatching means configured to match load impedance of one or moreantennae in a downhole probe to a characteristic impedance of atransmission line, in accordance with various embodiments of thisdisclosure. FIG. 4 includes a downhole probe (2) comprising a matchingmeans (6 b), a transmitting/receiving antenna (21) including tuningcapacitors (27), an array of one or more static magnetic fieldgenerating devices (20), a transmit/receive switch (22), a preamplifier(23), and a receive circuit matching means (28). A transmission line (5a) is coupled with transmitting/receiving antenna (21) via matchingmeans (6 b). A second transmission line (5 b) is coupled withtransmitting/receiving antenna (21) via transmit/receive switch (22),preamplifier (23) and receive circuit matching means (28).

The receive circuit matching means (28) may be configured to match anoutput impedance of downhole probe receive electronics, such as thepreamplifier (23) and/or buffer amplifier (not shown) in the receiveside of the downhole probe (2) to an impedance of the secondtransmission line (5 b) and/or or to an impedance of surface receiveelectronics (not shown) within the surface instrumentation (1) asreflected through the second transmission line (5 b). The secondtransmission line (5 b) may comprise an electrically long analog receivecable. A/D conversion and storage of the detected NMR signals may beperformed by receive electronics located at the surface, e.g., amongsurface instrumentation (1).

Embodiments according to FIG. 4 are useful for consolidating additionalreceive electronics, specifically A/D converter devices (14), at thesurface, e.g., among surface instrumentation (1). Stationing the A/Dconverters (14) at the surface simplifies their control andsynchronization by a surface-based controller (10), and potentiallyallows the downhole probe (2) to be smaller and simpler.

Referring to FIG. 1-FIG. 4, the downhole probe (2) contains a magnetassembly which causes alignment and polarization of NMR susceptiblespecies in the adjacent earth formation (4). The downhole probe (2) alsocontains a transmitting antenna (21 a) and a receiving antenna (21 b).In some embodiments these can be the same antenna (21).

The controller (10) at the surface is programmed to control digitaland/or analog signal generator devices (12), which produce appropriatelow-voltage signals for generation of NMR pulse sequences. The RF poweramplifier (13) at the surface is configured to convert the low voltageNMR pulse sequence signals from the signal generating devices (12) intohigher powered NMR pulse sequences. The output of the power amplifier(13) is generally load-dependent electrical current and voltagewaveforms, also referred to herein as RF current waveforms.

The transmitting antenna (21 a) within the downhole probe (2) iselectrically connected to the electrically-long transmission line (5 a),and is driven directly from the surface by the power amplifier (13),through the transmission line (5 a). The RF current waveforms aregenerated by the power amplifier (13) at the surface and transferred bythe transmission line (5 a) to the transmitting antenna (21 a) in thedownhole probe (2), which converts the electrical energy from the poweramplifier (13) into local Alternating Current (AC) magnetic fields whichactivate NMR processes in the earth formation (4).

One or more matching means (6 a, 6 b) are employed so as toapproximately match the output impedance of the power amplifier (13),through the transmission line (5 a), to the input impedance of thetransmitting antenna (21 a).

The receiving antenna (21 b) within the downhole probe (2) iselectrically connected to receive electronics within the downhole probe(2), such as preamplifier (23). One or more A/D converters (14), locatedeither in within the downhole probe (2) or at the surface, are used tosample and store detected NMR signals.

FIG. 5-FIG. 8 illustrate example impedance matching means comprising oneor more impedance matching circuits, in accordance with variousembodiments of this disclosure. The illustrated impedance matchingcircuits may be used for example as impedance matching means (6 a, 6 b)illustrated in FIG. 1-FIG. 4.

In general, FIG. 5 illustrates impedance matching circuits comprisingappropriate transformers configured to match impedances of both a poweramplifier (13) and a transmitting antenna (21 a) to a characteristicimpedance of a transmission line (5). FIG. 6 illustrates impedancematching circuits comprising a series inductor and parallel capacitorconfigured to match a relatively low output impedance of a poweramplifier (13) to a higher impedance transmission line (5). FIG. 7illustrates an impedance matching circuits comprising a series matchingcapacitor configured to match a relatively high input impedance of aparallel tuned transmitting antenna to a lower impedance transmissionline (5). FIG. 8 illustrates impedance matching circuits comprising atransformer-coupled pair of transmit and receive antennae configured tomatch a relatively high input impedance of a parallel tuned receiveantenna (coil) to a lower impedance transmission line (5) duringtransmit mode. During receive mode, optional series crossed diodes areconfigured to isolate the receive antenna (21 b) from the transmitantenna (21 a) and transmission line (5).

Impedance matching means may comprise the impedance matching circuitsillustrated in FIG. 5-FIG. 8, and variants thereof, comprisingtransformers, combinations of inductors and capacitors, or combinationsof transformers, inductors and capacitors. However, impedance matchingmeans are not limited to the illustrated impedance matching circuits.Impedance matching means may comprise any means to optimize theefficiency of transmitting waveforms, including transmit waveforms andreceived NMR response waveforms, through an electrically longtransmission line (5).

For example, impedance matching means may comprise any means to optimizethe efficiency of transmitting amplified RF NMR excitation waveforms,from a power amplifier (13) located at the surface, to a downhole probe(2), through an electrically long transmission line (5). There are manypossible ways to cause the output impedance of the power amplifier (13)to be approximately matched to the impedance of a downhole probeantenna, such as a transmitting antenna (21 a), a receiving antenna (21b), and/or a transmitting receiving antenna (21), as seen through theelectrically long transmission line (5).

In some embodiments, impedance matching means may comprise an NMRlogging apparatus design that is configured to match the outputimpedance of the power amplifier (13) to an input impedance of atransmitting antenna (21 a). For example, NMR logging apparatusimpedances may be matched to a common value Zo, where for example Zo maybe equal to 50 ohms, or 75 ohms. In some embodiments of this design, thepower amplifier (13) may be designed or selected to exhibit outputimpedance Zs equal to Zo, the long transmission line (5) would bedesigned or selected to exhibit a characteristic impedance of Zo, andthe downhole probe antenna assembly may be designed or selected toexhibit an input impedance Zl equal to Zo. In some embodiments, animpedance matching means may therefore comprise one or more antennae inthe downhole probe (2) that are configured to present a load impedanceapproximately equal to a characteristic impedance of the transmissionline (5) during transmit mode.

In some embodiments, impedance matching means may comprise a firstmatching means configured to match the output impedance of the poweramplifier (13) to a characteristic impedance of the transmission line(5), and a second matching means configured to match load impedance ofone or more antennae in the downhole probe (2) to the characteristicimpedance of the transmission line (5). For example, FIG. 5 illustratesthe use of a first matching means comprising a transformer configured tomatch the output impedance of a power amplifier (13) (with comparativelylow output impedance) to the impedance of a transmission line (5) withcomparatively high impedance. For example, a transformer with a turnsratio of 1 to 3.2 will transform an output impedance of 5 ohms toapproximately 50 ohms, to approximately match the impedance of a 50 ohmtransmission line (5). Similarly, FIG. 5 also depicts a second matchingmeans comprising a second transformer configured to match the inputimpedance of a transmitting antenna (21 a) to the characteristicimpedance of the transmission line (5). For example, as shown in FIG. 5,a transformer with a turns ratio of 2 to 9 will approximately match atransmitting antenna (21 a) input impedance of 1000 ohms to a 50 ohmtransmission line impedance.

In some embodiments, impedance matching means may be configured to usecollections of reactive circuit elements to match the output impedanceof the power amplifier (13) to the transmission line impedance, and/orto match the input impedance of a transmitting antenna (21 a) to thetransmission line impedance. For example, FIG. 6 illustrates animpedance matching circuit comprising a series inductor on the input,and a parallel capacitor on the output. The illustrated impedancematching circuit acts to match a low impedance input to a higherimpedance output at a particular frequency. In FIG. 6, the impedancematching circuit is illustrated in the application of matchingcomparatively low power amplifier output impedance of 5 ohms to acomparatively higher characteristic transmission line impedance of 50ohms. This type of impedance matching circuit may also be used to matchtransmitting antenna (21 a) impedance to transmission line impedance.

In some embodiments, impedance matching means may be configured to usereactive circuit elements as matching means, the reactive circuitelements comprising a series capacitor. For example, FIG. 7 illustratesan impedance matching circuit comprising a series capacitor configuredto match a comparatively high impedance of a parallel tuned transmittingantenna (21 a) to a comparatively low impedance of a transmission cable.

In some embodiments, impedance matching means may comprise atransformer-coupled antenna assembly configured to match the impedanceof a transmitting antenna (21 a) to the impedance of the transmissionline (5). For example, a transformer-coupled antenna assembly maycomprise two mutually coupled coils, a transmitting antenna (21 a)primary coil (which is electrically connected to the transmission line(5), and a receiving antenna (21 b) secondary coil which is notelectrically connected to the transmission line (5), but which functionsas the detection coil in receive mode. The primary and secondary coilsmay be configured with differing numbers of turns and/or incompletecoupling. In transmit mode, the secondary coil presents a load to thetransmission line (5), through mutual coupling with the primary coil.The turns ratio and/or coupling reduction factor cause the impedance ofthe secondary coil (21 b) to be transformed to a different value whenseen as a load on the primary coil input. This impedance transformingbehavior can be used to match the relatively high input impedance of aparallel tuned secondary coil (21 b) to the relatively lowcharacteristic impedance of the transmission line (5).

For example, FIG. 8 illustrates the use of a transformer-coupled antennaassembly to match the comparatively high impedance of the secondary coil(the detection coil) to the comparatively low impedance of thetransmission line (5). In the example of FIG. 8, the characteristicimpedance of the transmission line (5) is 50 ohms, the impedance of theparallel tuned receiving antenna (21 b) secondary coil is 1250 ohms, anda primary to secondary coil turns ratio of 1 to 5 serves to transformthe secondary coil impedance of 1250 ohms to approximately 50 ohms, thusmatching the secondary coil to the characteristic impedance of thetransmission line (5) in transmit mode. The optional series crosseddiodes depicted in FIG. 8 serve to isolate the secondary coil from thetransmitting antenna (21 a) primary coil and the transmission line (5),during receive mode only.

In some embodiments according to FIG. 8, separate transmit and receiveantennas may be employed, wherein the transmitting antenna (21 a) andreceiving antenna (21 b) may be inductively coupled with a non-zeromutual inductance during a transmit mode, and wherein the transmittingantenna (21 a) is inductively coupled to the receive antenna (21 b)during receive mode, and wherein the transmitting antenna (21 a) doesnot significantly load the receive antenna (21 b) during receive mode.For example, the one or more antennae (21 a, 21 b) in the downhole probe(2) may comprise a pair of inductively coupled loops, such that: a firstloop (21 a) is electrically connected to the transmission line (5), asecond loop (21 b) is electrically connected to a parallel tuningcapacitor, a transmit/receive switch, and receive electronics, and aratio of turns between the first and second loops is selected so as toapproximately or partially match a relatively high impedance of thesecond loop (21 b) to a relatively low impedance of the transmissionline (5).

In some embodiments, impedance matching means for matching the impedanceof a transmitting antenna (21 a) to the power amplifier (13) maycomprise an appropriately selected transmission line (5) length. Forexample, the length of the transmission line (5) may be approximatelyequal to one quarter of a wavelength, or any odd integer multiple ofquarter wavelengths, at an operating frequency of the NMR loggingapparatus. The transmitting antenna (21 a) and/or power amplifier (13)may be configured such that the transmitting antenna (21 a) impedance istransformed by the quarter wave transmission line to match the poweramplifier output impedance. A transmission line (5) that isapproximately one quarter of a wavelength in length at a particularoperating frequency will transform the impedance Z2 attached to one endof the transmission line (5) to another impedance value Z1 at the inputto the transmission line (5) according to the relation:|Zo|^2=Z1*Z2where Zo is the characteristic impedance of the transmission line (5),Z2 is the load impedance attached to one end of the transmission line(5), and Z1 is the input impedance seen at the other end of thetransmission line (5). This impedance transforming property also occursfor transmission line lengths equal to any odd integer multiple ofquarter wavelengths at an operating frequency of the NMR loggingapparatus.

In some embodiments using a quarter wavelength transmission line tomatch the power amplifier output impedance to the transmitting antenna(21 a) impedance, a power amplifier (13) and transmission line (5) maybe configured such that the power amplifier output impedance Z1 is equalto the square of the transmission line impedance Zo divided by the probeimpedance Z2:Z1=|Zo|^2/Z2

In some embodiments using a quarter wavelength transmission line tomatch the power amplifier output impedance to the transmitting antenna(21 a) input impedance, a transmitting antenna (21 a) and transmissionline (5) may be configured such that the transmitting antenna (21 a)input impedance Z2 is equal to the square of the transmission lineimpedance Zo divided by the power amplifier output impedance Z1:Z2=|Zo|^2/Z1

In some embodiments, impedance matching means for matching the impedanceof a transmitting antenna (21 a) to the impedance of the power amplifier(13) may comprise a half wavelength transmission line at an operatingfrequency of the NMR logging apparatus, optionally in conjunction withone or more means to match the transmitting antenna (21 a) impedance tothe power amplifier impedance. A transmission line (5) whose length isone half wavelength, or any integer multiple of half wavelengths, causesthe impedance attached to one end of the transmission line (5) to bereflected without changing on the other end of the transmission line(5), regardless of the characteristic impedance of the transmission line(5). Thus, a half wavelength transmission line can simplify the matchingproblem to any means that matches the output impedance of the poweramplifier (13) to the input impedance of the transmitting antenna (21a). Impedance matching means for use in conjunction with the halfwavelength transmission line may include any of the impedance matchingmeans described herein.

Because quarter and/or half wavelength transmission line lengths may beused as impedance matching means as described above, it will beappreciated that in general, impedance matching means may comprises atransmission line length that is approximately a positive integer numberof quarter wavelengths of a current and/or voltage waveform generated bythe power amplifier, whether the positive integer number is even or odd.

It will be appreciated with the benefit of this disclosure thatimpedance matching means described herein can be combined in many waysto achieve the purpose of matching the output impedance of the poweramplifier (13) to the input impedance of a transmitting antenna (21 a)via an electrically long transmission cable. For example, a quarterwavetransmission line can be used to achieve a portion of an impedancetransformation, and a remaining impedance transformation can beaccomplished by an appropriate transformer or other impedance matchingcircuit. Similarly, the impedance matching means described herein in thecontext of the power amplifier (13) and the transmitting antenna (21 a)may be applied in the context of the power amplifier (13) and atransmitting/receiving antenna (21). Also, the impedance matching meansdescribed herein in the context of the power amplifier (13) and thetransmitting antenna (21 a) may be applied in a receive circuit matchingmeans (28) as well as an impedance matching means deployed at an end ofa secondary transmission line (5 b) that is opposite the downhole probe(2), e.g., at receive electronics in the surface instrumentation (1).

FIG. 9 illustrates an example NMR logging apparatus comprising surfaceinstrumentation (1), a plurality of transmission lines (5), and aplurality of downhole probes (2), in accordance with various embodimentsof this disclosure. A plurality of downhole probes (2) and transmissionlines (5) are deployed in one or more earth boreholes (3) in an earthformation (4), and surface instrumentation (1) is configured to performNMR measurements using the plurality of downhole probes (2).

FIG. 10 illustrates an example NMR logging apparatus comprising surfaceinstrumentation (1), a plurality of transmission lines (5), a pluralityof downhole probes (2), and a switching device (7) coupled between thetransmission lines (5) and the power amplifier (13) to selectivelyconnect the power amplifier (13) to one or more of the transmissionlines (5), in accordance with various embodiments of this disclosure.

In FIG. 9 the surface instrumentation (1) may be configured to performNMR measurements using one or more of the plurality of downhole probes(2). The surface instrumentation (1) may be configured to produceappropriate transmitted NMR pulse sequences, which may be routed toindividual downhole probes (2) to perform localized NMR measurementswithin one or more of the earth boreholes (3). In some embodiments, thesurface instrumentation (1) may be configured to perform NMRmeasurements with the plurality of downhole probes (2) over a commoninterval of time in which two or more of the downhole probes (2) areused. As shown in FIG. 9, the surface instrumentation (1) may also beconfigured to perform NMR measurements with two or more of the pluralityof downhole probes (2) deployed in a single earth borehole.

Each downhole probe (2) may be connected to the surface instrumentation(1) via a transmission line or lines (5), optionally using one or moreof the impedance matching means described herein. Impedance matchingmeans need not be employed on the transmission lines (5). For example,impedance matching means need not be employed when transmission linelength is suitably short. The impedance matching means may be common toall downhole probes (2) and transmission lines (5), or unique to eachdownhole probe (2) and transmission line (5).

In some embodiments, surface instrumentation (1) may comprise a singlesurface instrumentation unit. In some embodiments, surfaceinstrumentation (1) may control one or more local surfaceinstrumentation units, e.g., by connecting to a communications network(6). Network-enabled surface instrumentation (1) may also enable thesurface instrumentation (1) and downhole probes (2) to operateautonomously, and/or from remote locations.

In some embodiments, switching between multiple downhole probes (2) bythe surface instrumentation (1) may be accomplished in a number of ways.First, transmission lines for individual downhole probes may be manuallyattached and detached from the surface instrumentation (1), viaappropriate electrical connections. This method facilitates moving thesurface instrumentation (1) from one location to another. Hence a singlesurface instrumentation unit (1) can be used to perform NMR measurementsusing embedded in-situ downhole probes (2) in multiple locationsseparated by great distances, potentially as far away as differentcontinents.

Another method for switching between different downhole probes (2) bythe surface instrumentation (1) is to use a switching device (7) coupledbetween the plurality of transmission lines (5) and the power amplifier(13), as depicted in FIG. 10. Switching device (7) may comprise aplurality of electrical switches, whereby switching device (7) may beconfigured to selectively connect the power amplifier (13) to one ormore of the transmission lines (5). The switches may be manually orelectrically activated, and may be controlled by a human operator or acomputer, such as controller (10). In some embodiments, surfaceinstrumentation (1) may be configured to control the switches of theswitching device (7) as appropriate, to perform measurements with one ormore of the downhole probes (2). Appropriate impedance matching meansmay be implemented on either side of each switch in a switching device(7), or on either side of the switching device (7) as a whole, asappropriate for particular embodiments.

In some embodiments, a method for performing NMR measurements within anearth borehole (3) or in earth formations (4) adjacent to an earthborehole, may comprise deploying a plurality of downhole probes (2) withassociated transmission lines (5) within a plurality of boreholes (3),and/or at a plurality of locations within a single borehole, anddeploying a single surface instrumentation unit or a number of surfaceinstrumentation units less than the number of deployed downhole probes(2) to perform NMR measurements in conjunction with the deployeddownhole probes (2). In some embodiments, the surface instrumentationunit or units may be programmed to perform multiple NMR measurements onmultiple deployed downhole probes (2) over a common period of time. Insome embodiments, the surface instrumentation (1) may be connected to acomputer or communications network (6) and monitoring and/or control ofNMR measurements may be performed at least in part by human operators atlocations remote to the surface instrumentation (1), such as inside anearby building, or at a location many miles from the location of thesurface instrumentation (1).

In some embodiments, one or more downhole probes (2) and transmissionlines (5) may be deployed in one or more boreholes (3) and left in saidboreholes (3) for significant periods of time, such as weeks, months, oryears, so as to enable repeated NMR measurements of the subsurfaceproperties over intervals of time.

In some embodiments, long term NMR monitoring methods may be carried outusing NMR logging apparatus described herein. One or more downholeprobes (2) and transmission lines (5) may be left in place for extendedperiods of time, such as weeks, months, or years, and surfaceinstrumentation (1) may be periodically or continuously attached to theone or more transmission lines (5). NMR measurements may be performed bythe NMR logging apparatus at various intervals throughout the extendedperiod of time. Long term monitoring has important applicationsincluding the monitoring of subsurface contamination, monitoring theremediation of subsurface contamination including bioremediation,monitoring of changes in moisture content in the unsaturated zone,monitoring of formations subject to extraction of oil, gas, water orother commodities, and monitoring of formations subject to injection ofcarbon dioxide, water or other substances.

In some embodiments, surface instrumentation (1) may be deployed withina mine, cave, underground structure, or other man made or natural cavitywithin the earth. The surface instrumentation (1) may be deployed andoperated within the subsurface cavity and the transmission lines (5) anddownhole probes (2) may be deployed into one or more boreholes openinginto the subsurface cavity.

There is little distinction left between hardware and softwareimplementations of aspects of systems; the use of hardware or softwareis generally (but not always) a design choice representing cost vs.efficiency tradeoffs. There are various vehicles by which processesand/or systems and/or other technologies described herein can beeffected (e.g., hardware, software, and/or firmware), and that thepreferred vehicle may vary with the context in which the processesand/or systems and/or other technologies are deployed. For example, ifan implementer determines that speed and accuracy are paramount, theimplementer may opt for a mainly hardware and/or firmware vehicle; ifflexibility is paramount, the implementer may opt for a mainly softwareimplementation; or, yet again alternatively, the implementer may opt forsome combination of hardware, software, and/or firmware.

The foregoing detailed description has set forth various embodiments ofthe devices and/or processes via the use of block diagrams, flowcharts,and/or examples. Insofar as such block diagrams, flowcharts, and/orexamples contain one or more functions and/or operations, it will beunderstood by those within the art that each function and/or operationwithin such block diagrams, flowcharts, or examples can be implemented,individually and/or collectively, by a wide range of hardware, software,firmware, or virtually any combination thereof. In one embodiment,several portions of the subject matter described herein may beimplemented via Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs), digital signal processors (DSPs), orother integrated formats. However, those skilled in the art willrecognize that some aspects of the embodiments disclosed herein, inwhole or in part, can be equivalently implemented in integratedcircuits, as one or more computer programs running on one or morecomputers (e.g., as one or more programs running on one or more computersystems), as one or more programs running on one or more processors(e.g., as one or more programs running on one or more microprocessors),as firmware, or as virtually any combination thereof, and that designingthe circuitry and/or writing the code for the software and or firmwarewould be within the skill of one skilled in the art in light of thisdisclosure. In addition, those skilled in the art will appreciate thatthe mechanisms of the subject matter described herein are capable ofbeing distributed as a program product in a variety of forms, and thatan illustrative embodiment of the subject matter described hereinapplies regardless of the particular type of signal bearing medium usedto actually carry out the distribution. Examples of a signal bearingmedium include, but are not limited to, the following: a recordable typemedium such as a floppy disk, a hard disk drive, a Compact Disc (CD), aDigital Video Disk (DVD), a digital tape, a computer memory, etc.; and atransmission type medium such as a digital and/or an analogcommunication medium (e.g., a fiber optic cable, a waveguide, a wiredcommunications link, a wireless communication link, etc.).

Those skilled in the art will recognize that it is common within the artto describe devices and/or processes in the fashion set forth herein,and thereafter use engineering practices to integrate such describeddevices and/or processes into data processing systems. That is, at leasta portion of the devices and/or processes described herein can beintegrated into a data processing system via a reasonable amount ofexperimentation. Those having skill in the art will recognize that atypical data processing system generally includes one or more of asystem unit housing, a video display device, a memory such as volatileand non-volatile memory, processors such as microprocessors and digitalsignal processors, computational entities such as operating systems,drivers, graphical user interfaces, and applications programs, one ormore interaction devices, such as a touch pad or screen, and/or controlsystems including feedback loops and control motors (e.g., feedback forsensing position and/or velocity; control motors for moving and/oradjusting components and/or quantities). A typical data processingsystem may be implemented utilizing any suitable commercially availablecomponents, such as those typically found in datacomputing/communication and/or network computing/communication systems.The herein described subject matter sometimes illustrates differentcomponents contained within, or connected with, different othercomponents. It is to be understood that such depicted architectures aremerely exemplary, and that in fact many other architectures can beimplemented which achieve the same functionality. In a conceptual sense,any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality can be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermediate components. Likewise, any two componentsso associated can also be viewed as being “operably connected”, or“operably coupled”, to each other to achieve the desired functionality,and any two components capable of being so associated can also be viewedas being “operably couplable”, to each other to achieve the desiredfunctionality. Specific examples of operably couplable include but arenot limited to physically mateable and/or physically interactingcomponents and/or wirelessly interactable and/or wirelessly interactingcomponents and/or logically interacting and/or logically interactablecomponents.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to inventions containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should typically be interpreted to mean “atleast one” or “one or more”); the same holds true for the use ofdefinite articles used to introduce claim recitations. In addition, evenif a specific number of an introduced claim recitation is explicitlyrecited, those skilled in the art will recognize that such recitationshould typically be interpreted to mean at least the recited number(e.g., the bare recitation of “two recitations,” without othermodifiers, typically means at least two recitations, or two or morerecitations). Furthermore, in those instances where a conventionanalogous to “at least one of A, B, and C, etc.” is used, in generalsuch a construction is intended in the sense one having skill in the artwould understand the convention (e.g., “a system having at least one ofA, B, and C” would include but not be limited to systems that have Aalone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). In those instances where aconvention analogous to “at least one of A, B, or C, etc.” is used, ingeneral such a construction is intended in the sense one having skill inthe art would understand the convention (e.g., “a system having at leastone of A, B, or C” would include but not be limited to systems that haveA alone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). It will be furtherunderstood by those within the art that virtually any disjunctive wordand/or phrase presenting two or more alternative terms, whether in thedescription, claims, or drawings, should be understood to contemplatethe possibilities of including one of the terms, either of the terms, orboth terms. For example, the phrase “A or B” will be understood toinclude the possibilities of “A” or “B” or “A and B.”

While various embodiments have been disclosed herein, other aspects andembodiments will be apparent to those skilled in art.

The invention claimed is:
 1. A Nuclear Magnetic Resonance (NMR) loggingapparatus, comprising: surface instrumentation comprising a poweramplifier configured to generate one or more current and/or voltagewaveforms; a plurality of transmission lines coupled with the poweramplifier; and a plurality of downhole probes configured to fit withinone or more earth boreholes, each downhole probe comprising: one or morestatic magnetic field generation devices; and one or more antennaecoupled with a transmission line of the plurality of transmission lines;and at least one impedance matching means configured to match an outputimpedance of the power amplifier through at least one transmission lineto a load impedance of at least one antenna in at least one downholeprobe, wherein the at least one impedance matching means comprises afirst matching means configured to match the output impedance of thepower amplifier to a characteristic impedance of the at least onetransmission line, and a second matching means configured to match loadimpedance of the at least one antenna in the at least one downhole probeto the characteristic impedance of the at least one transmission line.2. The NMR logging apparatus of claim 1, wherein the at least onetransmission line has a length at least one tenth of one wavelength of acurrent and/or voltage waveform generated by the power amplifier.
 3. TheNMR logging apparatus of claim 1, wherein the surface instrumentationfurther comprises a controller and receive electronics configured toperform NMR measurements with the plurality of downhole probes.
 4. TheNMR logging apparatus of claim 1, wherein at least one of the staticmagnetic field generation devices comprises one or more permanentmagnets.
 5. The NMR logging apparatus of claim 1, wherein the at leastone downhole probe comprises means for coupling energy from the at leastone transmission line into the at least one antenna.
 6. The NMR loggingapparatus of claim 1, wherein the at least one downhole probe comprisesmeans for detecting NMR signals induced in the at least one antenna. 7.The NMR logging apparatus of claim 1, further comprising a switchingdevice coupled between the plurality of transmission lines and the poweramplifier, wherein the switching device is configured to selectivelyconnect the power amplifier to one or more of the transmission lines. 8.A Nuclear Magnetic Resonance (NMR) measurement method, comprising:deploying surface instrumentation on or above a surface of the earth,said surface instrumentation comprising a power amplifier configured togenerate one or more current and/or voltage waveforms; deploying aplurality of downhole probes inside one or more earth boreholes;deploying a plurality of transmission lines configured to transfercurrent and/or voltage waveforms between the power amplifier and thedownhole probes, wherein at least one transmission line is coupled withat least one impedance matching means configured to match an outputimpedance of the power amplifier through the at least one transmissionline to a load impedance of at least one antenna in at least onedownhole probe, wherein the at least one impedance matching meanscomprises a first matching means configured to match the outputimpedance of the power amplifier to a characteristic impedance of the atleast one transmission line, and a second matching means configured tomatch load impedance of the at least one antenna in the at least onedownhole probe to the characteristic impedance of the at least onetransmission line; and using the surface instrumentation and downholeprobes coupled via the transmission lines to perform NMR measurements ofone or more properties within and/or surrounding the one or more earthboreholes.
 9. The NMR logging apparatus of claim 8, wherein the at leastone transmission line has a physical length equal to or greater than onetenth of one wavelength of a current and/or voltage waveform within theat least one transmission line.
 10. The method of claim 8 furthercomprising using the at least one downhole probe to perform a pluralityof NMR measurements at a same location in an earth borehole, whereinsaid plurality of NMR measurements are separated in time.
 11. The methodof claim 10 further comprising using the plurality of NMR measurementsto detect a change over time of the one or more properties.
 12. Themethod of claim 11 wherein the one or more properties comprise one ormore of NMR properties, Nuclear Quadrupole Resonance (NQR) properties,physical properties, hydraulic properties, or chemical properties.
 13. ANuclear Magnetic Resonance (NMR) logging apparatus, comprising: surfaceinstrumentation comprising a power amplifier configured to generate oneor more current and/or voltage waveforms; a plurality of transmissionlines coupled with the surface instrumentation; and a plurality ofdownhole probes, each downhole probe coupled with one or more of thetransmission lines, each downhole probe configured to fit within one ormore earth boreholes, and each downhole probe comprising: one or morestatic magnetic field generation devices; and one or more antennae; andat least one impedance matching means configured to match an outputimpedance of the power amplifier through at least one transmission lineto a load impedance of at least one antenna in at least one downholeprobe, wherein the impedance matching means comprises a transmissionline length that is approximately a positive integer number of quarterwavelengths of a current and/or voltage waveform generated by the poweramplifier.
 14. The NMR logging apparatus of claim 13, further comprisinga switching device coupled between the plurality of transmission linesand the surface instrumentation, wherein the surface instrumentation isadapted to control the switching device to selectively connect to one ormore of the transmission lines.
 15. The NMR logging apparatus of claim13, wherein the surface instrumentation further comprises a controllerand an output signal generator, wherein the controller is adapted tocontrol the output signal generator to produce low voltage NMR pulsesequence activating signals as inputs to the power amplifier, andwherein the power amplifier is configured to generate current and/orvoltage waveforms for transmission through one or more of thetransmission lines to one or more of the downhole probes.
 16. The NMRlogging apparatus of claim 15, wherein the power amplifier is configuredto produce peak power of 2 kW or higher.
 17. The NMR logging apparatusof claim 13, wherein the at least one transmission line has a length atleast one tenth of one wavelength of a current and/or voltage waveformgenerated by the power amplifier.
 18. The NMR logging apparatus of claim13, wherein the at least one impedance matching means further comprisesa first matching means configured to match the output impedance of thepower amplifier to a characteristic impedance of the at least onetransmission line, and a second matching means configured to match loadimpedance of the at least one antenna in the at least one downhole probeto the characteristic impedance of the at least one transmission line.19. The NMR logging apparatus of claim 1, wherein the at least oneimpedance matching means includes a matching circuit comprisingtransformers, combinations of inductors and capacitors, or combinationsof transformers, inductors and capacitors.
 20. The NMR logging apparatusof claim 1, wherein the at least one impedance matching means comprisesa transmission line length that is approximately a positive integernumber of quarter wavelengths of a current and/or voltage waveformgenerated by the power amplifier.
 21. The NMR logging apparatus of claim1, wherein the at least one impedance matching means comprises one ormore antennae in the at least one downhole probe that are configured topresent a load impedance approximately equal to a characteristicimpedance of the at least one transmission line during a transmit mode.22. The NMR logging apparatus of claim 13, wherein the surfaceinstrumentation further comprises a power supply adapted to power thesurface instrumentation and one or more of the downhole probes.
 23. TheNMR logging apparatus of claim 13, wherein the surface instrumentationfurther comprises receive electronics, the receive electronicscomprising one or more Analog to Digital (A/D) converters configured toconvert NMR response signals received from downhole probes from analogto digital form, and the receive electronics comprising one or morememories configured to store digitized NMR response data.
 24. The NMRlogging apparatus of claim 23, further comprising at least one secondtransmission line coupled with the at least one downhole probe, whereinthe at least one second transmission line is configured to transmitdetected NMR signals from the at least one downhole probe to the receiveelectronics.
 25. The NMR logging apparatus of claim 13, wherein at leastone static magnetic field generation device in the at least one downholeprobe includes a permanent magnet or an electromagnet.
 26. The NMRlogging apparatus of claim 13, wherein the at least one antenna in theat least one downhole probe includes a transmit/receive antennaconfigured to generate NMR excitation fields during a transmit mode, andto detect NMR signals in a receive mode.
 27. The NMR logging apparatusof claim 13, wherein the at least one downhole probe comprises: one ormore permanent magnets; a transmitting antenna which is electricallyconnected to the at least one transmission line; a receiving antennawhich is electrically connected to receive electronics via atransmit/receive switch; and wherein the transmitting antenna andreceiving antenna are inductively coupled with a non-zero mutualinductance during a transmit mode.
 28. The NMR logging apparatus ofclaim 13, wherein the at least one downhole probe comprises apreamplifier adapted to amplify NMR signals detected at the at least onedownhole probe, and a transmit/receive switch to switch the at least onedownhole probe between a transmit mode and a receive mode.
 29. The NMRlogging apparatus of claim 13, wherein the NMR logging apparatus isconfigured to perform NMR measurements with the plurality of downholeprobes over a common interval of time in which two or more of thedownhole probes are used.
 30. The NMR logging apparatus of claim 13,wherein the NMR logging apparatus is configured to perform NMRmeasurements with two or more of the plurality of downhole probesdeployed in a single earth borehole.
 31. The NMR logging apparatus ofclaim 13, wherein the NMR logging apparatus is configured to perform NMRmeasurements with two or more of the plurality of downhole probesdeployed in multiple different earth boreholes.
 32. The NMR loggingapparatus of claim 13, wherein the at least one downhole probe is lessthan 5 inches in diameter.